man > tc-fq_codel(8)

FQ_CoDel(8)                                     Linux                                    FQ_CoDel(8)

NAME
       CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel)

SYNOPSIS
       tc  qdisc ... fq_codel [ limit PACKETS ] [ flows NUMBER ] [ target TIME ] [ interval TIME ] [
       quantum BYTES ] [ ecn | noecn ] [ ce_threshold TIME ] [ ce_threshold_selector VALUE/MASK ]  [
       memory_limit BYTES ]


DESCRIPTION
       FQ_Codel  (Fair  Queuing  Controlled  Delay) is queuing discipline that combines Fair Queuing
       with the CoDel AQM scheme. FQ_Codel uses a stochastic model to classify incoming packets into
       different flows and is used to provide a fair share of the bandwidth to all the  flows  using
       the  queue.  Each  such  flow is managed by the CoDel queuing discipline. Reordering within a
       flow is avoided since Codel internally uses a FIFO queue.


PARAMETERS
   limit
       has the same semantics as codel and is the hard limit on the  real  queue  size.   When  this
       limit is reached, incoming packets are dropped. Default is 10240 packets.


   memory_limit
       sets  a  limit on the total number of bytes that can be queued in this FQ-CoDel instance. The
       lower of the packet limit of the limit parameter and the memory limit will be  enforced.  De‐
       fault is 32 MB.



   flows
       is  the number of flows into which the incoming packets are classified. Due to the stochastic
       nature of hashing, multiple flows may end up being hashed into the  same  slot.  Newer  flows
       have  priority  over older ones. This parameter can be set only at load time since memory has
       to be allocated for the hash table.  Default value is 1024.


   target
       has the same semantics as codel and is the acceptable minimum standing/persistent  queue  de‐
       lay.  This minimum delay is identified by tracking the local minimum queue delay that packets
       experience. Default value is 5ms.


   interval
       has the same semantics as codel and is used to ensure that the measured  minimum  delay  does
       not  become too stale.  The minimum delay must be experienced in the last epoch of length in‐
       terval.  It should be set on the order of the worst-case RTT through the bottleneck  to  give
       endpoints sufficient time to react. Default value is 100ms.


   quantum
       is  the  number  of  bytes used as 'deficit' in the fair queuing algorithm. Default is set to
       1514 bytes which corresponds to the Ethernet MTU plus the hardware header length of 14 bytes.


   ecn | noecn
       has the same semantics as codel and can be used to mark packets instead of dropping them.  If
       ecn has been enabled, noecn can be used to turn it off and vice-a-versa. Unlike codel, ecn is
       turned on by default.


   ce_threshold
       sets  a threshold above which all packets are marked with ECN Congestion Experienced. This is
       useful for DCTCP-style congestion control algorithms that require  marking  at  very  shallow
       queueing thresholds.


   ce_threshold_selector
       sets  a  filter  so  that the ce_threshold feature is applied to only a subset of the traffic
       seen by the qdisc. If set, the MASK value will be applied as  a  bitwise  AND  to  the  diff‐
       serv/ECN byte of the IP header, and only if the result of this masking equals VALUE, will the
       ce_threshold logic be applied to the packet.


   drop_batch
       sets  the  maximum  number of packets to drop when limit or memory_limit is exceeded. Default
       value is 64.


EXAMPLES
       #tc qdisc add   dev eth0 root fq_codel
       #tc -s qdisc show
       qdisc fq_codel 8002: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514
        target 5.0ms interval 100.0ms ecn
          Sent 428514 bytes 2269 pkt (dropped 0, overlimits 0 requeues 0)
          backlog 0b 0p requeues 0
           maxpacket 256 drop_overlimit 0 new_flow_count 0 ecn_mark 0
           new_flows_len 0 old_flows_len 0

       #tc qdisc add dev eth0 root fq_codel limit 2000 target 3ms interval 40ms noecn
       #tc -s qdisc show
       qdisc fq_codel 8003: dev eth0 root refcnt 2 limit 2000p flows 1024 quantum 1514 target  3.0ms
       interval 40.0ms
        Sent 2588985006 bytes 1783629 pkt (dropped 0, overlimits 0 requeues 34869)
        backlog 0b 0p requeues 34869
         maxpacket 65226 drop_overlimit 0 new_flow_count 73 ecn_mark 0
         new_flows_len 1 old_flows_len 3



SEE ALSO
       tc(8), tc-codel(8), tc-red(8)


AUTHORS
       FQ_CoDel  was  implemented  by  Eric  Dumazet. This manpage was written by Vijay Subramanian.
       Please report corrections to the Linux Networking mailing list <netdev AT vger.org>.

iproute2                                     4 June 2012                                 FQ_CoDel(8)